Teeth grinding in 9-month-old babies may be a normal phenomenon due to teething in children, and it may also be caused by intestinal parasitic infection. 1. Physiological factors: during the child’s teething, the roots of the teeth may feel a slight itch, in which case the 9-month-old baby will appear to grind his teeth, which is a normal phenomenon. 2. Intestinal parasite infection: 9-month-old babies with intestinal parasite infection may experience teeth grinding at night when the parasite is active, which is due to the parasite’s activity stimulating the human body’s nerves, causing nerve excitation leading to the phenomenon. After eliminating the physiological factors, if the symptoms of teeth grinding in 9-month-old babies persist without relief, please consult the doctor promptly to find out the cause and ask the doctor to deal with it.